The proposed research would continue our investigation of the perception of time-varying (frequency modulated) complex signals by normal-hearing listeners. Our basic two-component complex tones represent the elementary signals in Voelcker's formulation of a unified modulation theory. More complex modulated signals can be represented in terms of these elementary ones. We have established that the pitch of a given two-component complex is related to an average of the instantaneous frequency fluctuations within that signal. Further, we have shown that the discriminability of a pair of complementary two-component complex tones is based upon their difference in a weighted average of instantaneous frequency. In this part of the investigation we plan to determine the "internal representation" of our two-component signals by using them as maskers in a conventional direct masking test. We plan to further our understanding of the discrimination process by determining the influence of signal presentation level and signal duration on the discriminability of two-component complex signals. Finally, we plan to extend the study of the low pitch of complex tones to the determination of the pitch of quasi-vowel sounds.